High efficiency plasma processing head including a diffuser having an expanding diameter



J. T. NAFF Sept. 3, 1968 3,400,070 HIGH EFFICIENCY PLASMA PROCESSING HEAD mcmmme A DIFFUSER HAVING AN EXPANDING DIAMETER 2 Sheets-Sheet 1 Filed June 14, 1966 INVENTOR. g/bmv 15M MQFF firroelwsys.

Sept. 3, 1968 J. T. NAFF 3,400,070

HIGH EFFICIENCY PLASMA PROCESSING HEAD INCLUDING A DIFFUSER HAVING AN EXPANDING DIAMETER Filed June 14, 1965 2 Sheets-Sheet 2 V INVENTOR- 65 4Q FEE/M7614 MFA 3,400,070 HIGH EFFICIENCY PLASMA PROCESSING HEAD INCLUDING A DIFFUSER HAVING AN EXPAND- ING DIAMETER John Tom Naif, Costa Mesa, Calif., assignor, by mesne assignments, to Hercules Incorporated, New Castle County, Del., a corporation of Delaware Filed June 14, 1965, Ser. No. 463,799 17 Claims. (Cl. 204-311) This invention relates generally to high temperature electric arc plasma processing, and more particularly has to do with substantial improvements in methods of plasma processing of fluids and solids and also with improvements in plasma electric arc head structures.

In the past, typical plasma arc jet devices have included a centrally located anode rod and an annular cathode surrounding the rod. An electrical arc passes from the cathode to the anode and feed materials as well as gas are fed generally unidirectionally in the arc region. Such devices have many disadvantages, among which are included excessive electrode erosion at thermionic temperatures occurring -at high currents and pressures as Well as low currents and pressures; disadvantageously high peak to peak current fluctuation; the need to employ an expensive tungsten cathode in order to reduce the rate of erosion; the need to separately inject different reactants into the are at spaced locations in order to reduce electrode clogging and erosion rates; the problem of cathode destruction and clogging when hydrocarbons are introduced into the arc; and all of the foregoing imposing limitations on scale up of the head to handle higher power requirements, so that power as high as one megawatt for example could not be utilized.

It is a major object of the present invention to provide improvements in method and apparatus by which the above mentioned disadvantages may be overcome.

In its method aspects, the invention concerns the establishment of an arc discharge pattern to penetrate and bridge flow passing passages within both cathode and anode elements, and supplying gas under pressure to flow through the arc pattern or region in the element passages to unstabilize the loci of arc attachment to both electrode elements. Typically, the passages in each of the electrode elements are cylindrical, conical, or have reduced upstream cross sectional region and enlarged downstream cross sectional region, and the process includes controlling the gas supply to sweep the arc unstabilized attachment locus downstream in the cylindrical electrodes, or into the enlarged cross sectional region in each electrode element of other configuration whereby more electrode area is presented for increasing the instability of the arc attachment and thereby increasing electrode life. Other steps of the method include controllably quenching the hot gas flowing downstream of the arc attachment loci; variably controlling the ditferential rate of downstream flow of gas from the passages; and swirling the supplied gas approaching said passages.

In its apparatus aspects, the invention is embodied in structure including anode and cathode elements forming passages for passing the flow of gas therethrough and for reception of an arc discharge pattern penetrating the elements in the path of gas flow, and means to conduct electrical current to the elements to create the are discharge pattern. Typically, each of the cathode and anode elements forms a gas discharge passage, and gas inlet porting extends between the cathode and anode elements and in such proximity to the electrode element passages that the inlet flow divides to enter the respective passages. Additional features include the provision of annular electrode elements forming gas flow passages that extend downstream, and typically symmetrically (although non-symited States Patent U 3,400,070 Patented Sept. 3, 1968 metrical passages are also contemplated), at opposite sides of the inlet flow division locus, the provision for vortex as well as radial injection of the inlet flow of gas to maintain arc attachment inst-ability in both electrode passages; the provision for gas flow passages in the electrodes characterized in that the passage has a relatively reduced diameter throat region directly downstream of the flow division locus from the interior of which the arc attachment locus is swept downstream into a relatively increased diameter diffuser region wherein the arc has attachment to the electrode; the provision of means to introduce quench fluid into the path of the hot gas flowing downstream relative to the loci of arc attachment in both electrodes; the provision for variably controlling downstream flow of gas from at least one of the electrodes; and provision for recombination of the divided flow of gas exiting from the electrodes.

Among the unusually advantageous results flowing from. the invention are the enablement of use of a much higher voltage are for higher power output, as for example in the megawatt range; the elimination of need in many applications for an expensive tungsten electrode; the facilitation of use of cathode and anode elements made of the same materials, as for example copper; the simplification of the cathode as well as anode arc attachment regions without necessarily resorting to eflicient thermionic emitters for cathode materials; the facilitation of scale-up for large gas throughputs and high power requirements, as a result of the head configuration and functioning thereof; simplified construction of the head structure because of symmetry; enablement of operation at much higher gas pressures and ability to handle an extremely large variety of materials directly through the arc column without adverse effects; better control of current and pressure and less peak to peak current fluctuations; facilitation of operation at significantly higher percentage of open circuit voltage so that a smaller capacity power supply is needed; and better control of quenching.

These and other objects and advantages of the invention, as well as the details of illustrative embodiments, will be more fully understood from the following detailed description of the drawings in which:

FIG. 1 is a vertical cross section taken through one form of plasma processing apparatus incorporating the invention;

FIG. 2 is an enlarged vertical cross section taken in the same plane as FIG. 1, but showing a typical are discharge pattern;

FIGS. 35 are cross sections taken on line 3-3, 44 and 5- 5 of FIG. 2;

FIG. 6 is a view like FIG. 3 but showing radial instead of tangential injection paths for the inlet gas flow; and

FIGS. 7 and 8 show further modified forms of the invention.

The drawings illustrate one form of structure including anode and cathode elements forming passages for passing the flow of gas t-herethrough and for reception of an arc discharge pattern penetrating the elements in the path of the flow. For example, annular cathode and anode elements are provided at 10 and 11 to have coaxial passages 12 and 13 for passing the flow of gas in the direction of arrows 14 and 15. Elements 10 and 11 may advantageously be made of copper, or other conductive materials.

The structure also forms gas flow inlet portion extending between the cathode and element and in such proximity to the passages 12 and 13 that the inlet flow divides to enter the respective passages. Typically, a fluorocarbon gas ring 16 provides a series of inlet ports 17 arranged as seen in FIG. 3 to receive gas from duct 22 and plenum 22a to direct the inlet flow in a spiral or vortex within a plenum 18 between the anode and cathode terminal flanges 19 and 20. The vortex flow divides at the locus 21 and enters the 3 relatively reduced diameter throat regions 12a and 13a of passages 12 and 13. The latter also typically include relatively increased diameter diffuser regions 12b and 13b downstream of the throat regions.

The above-mentioned structure is illustrated as centered within the bore 24 of a housing 25, appropriate O-ring seals being provided at 26, 27, 28 and 29 between the bore 24 and terminal flanges 19, 20, 30 and 31 of the electrodes. Fluid coolant passages 32, 33, 34 and 35 are formed be tween the electrodes and the housing, both inwardly and outwardly of ported heat conductor bodies 36 and 37 centered within bore 24. Coolant fluid may enter passages 32 and 34 via ducts 38 and 39, circulate into and out of passages 33 and 35, and exit vi-a ducts 40 and 41.

Further in accordance with the invention, an arc discharge pattern penetrates both the electrode elements in the path of gas flow therein, producing a gas unstabilized are particularly at the points of variable are attachment to the electrodes. One such pattern is generally indicated by the lines 42 in FIG. 2, which pass axially endwise through the passage portions 12a and 13a. and variably attach to the electrodes at the enlarged diffuser regions 12b and 1312. Such variable or unstable attachment is promoted due to the velocity of flow of the gas over the electrodes, and the vortex or rotating character of such flow. Also, the enlargement of the passages at 12b and 130 provides greater area for the arc to play over, thereby reducing any tendency for high temperature erosion of the electrode surface. Typically, the are oscillates between the different are attach- From regions 60 and 61 in piping 64 and 65 the two streams of discharge gas may be recombined as indicated by flow lines 66 and 67, or they may be separately withdrawn as indicated by flow lines 68 and 69. In either event, flow control valves 7073 in such flow lines are operable to variably control the discharge flow of gas from the apparatus. Also, the inlet flow of gas to duct 22 may be controlled as to flow rate and pressure by valve 74 or other means in order to control the arc discharge pattern, as for example sweeping the arc attachment loci relatively downstream or upstream in passages 12 and 13, i.e. typically from narrow throat regions 12a and 13a into enlarged diffuser sections 12b and 13b. Bolts 76 and 77 may attach the pipe retainers 78 and 79 to the bodies 48 and 49 respectively.

In FIG. 6 is shown an alternate form of fluorocarbon gas inlet ring 16a providing radial instead of tangential inlet ports 17a for the inflowing reaction gas. Accordingly, the flow does not spiral or rotate in the passages 12 and 13; however, the downstream valves 71-73 may then be adjusted to provide for turbulent flow conditions in the passages 12 and 13 acting to unstabilize the arc attachment loci.

In actual operation of the form of the invention seen in FIGS. l-5, natural gas was fed into the reaction to produce acetylene, and a yield concentration of 13.5% was obtained at the rate of 4.06 kilowatt hours of power expended per pound of produced acetylene. The following tabulation indicates the results for various runs:

TYPICAL OPERATING PARAMETE RS FOR SMALL SIZE VERSION OF HEAD Run N o 1 2 3 4 5 Open circuit Voltage 800 800 800 800 800 Running voltage 440 444 550 565 610 Running current. 120 220 190 160 180 Input power, kW 52. 8 97 105 91 110 Natural gas flow (standard cub feet per hour) 815 830 680 995 1640 Hydrogen gas flow (s.c.f.h.) 0 0 1040 203 360 Pressure at input to swirl gas ring, p.s.i.g 46 60 81 72 85 Exit pressure measured downstream of electrode (p.s.i.g.) 0 0 50 42. 5 44 Percent acetylene in product gas 13. 5 14. 2 7. (3 11.0 7. 6

ment points illustrated. The surface temperature of the electrodes at the points of arc attachment may be kept well below the melting temperature of copper, so that formation of copper carbide is largely avoided where the gas contains hydrocarbons or carbon containing gases.

Means to conduct electrical current to the electrode elements in order to provide for creation of such an advantageously unstable arc discharge pattern may include electrically conductive connector plate 44 and 45 having connection at 46 and 47 to the electrode terminal flanges 30 and 31. Further, plates 44 and 45 may be retained at opposite ends of the housing 25 by annular bodies 48 and 49 bolted at 50 to the plates and housing. A source of direct or alternating current and voltage is indicated at 51 with terminal connection at 52 and 53 to the respective plates 44 and 45.

A further feature of the invention has to do with the provision of means to introduce quench fluid into the path of hot gas flowing downstream relative to the loci of arc attachment. One such means as shown in the drawings includes the bodies 48 and 49 forming plenum chambers 54 and 55 to which quench fluid is supplied via ducts 56 and 57. From such chambers the quench fluid, typically consisting of water or other suitable medium, passes via ports 58 and 59 into the gas at regions 60 and 61 downstream of the arc attachment loci. The quench fluid operates to sharply reduce the temperature of the gas flow to aid in terminating or reducing high temperature chemical reactions occurring therein. Valves 62 and 63 are operable to control the rate of quench fluid introduction to regions 60 and 61. Quenching may also be effected by means of water or other quench medium passages placed directly in the electrodes 10 and 11 downstream of the arc attachment loci.

FIG. 2 illustrates a supplementary feed path or ducting for direct injection of reactant into the are at a point downstream of flow division locus 21. This is of unusual advantage where the reactant consists of particulate material, as for example iron ore, to produce a product of desired metallurgical properties.

Referring to FIG. 7, a magnetic field producing coil is seen at extending about an electrode 121 of the type disclosed at 11 in FIG. 2. The coil is controllably energized from a source 122 so as to effect rotation of the locus of arc attachment within the passage enlargement 123, as for example where radial injection is used as described in FIG. 6, and including powder. Also, means is seen at 124, typically including a duct 125 and injector nozzle 126 in electrode 121 for introducing quench fluid into the path of hot gas flowing downstream relative to the locus of arc attachment.

Referring to FIG. 8, magnetic field producing coils are seen at 128 and 129 extending about electrodes 130 and 131. Electrode 130 is like that disclosed at 10 in FIG. 2; however electrode 131 differs in that it is unsymmetrical with respect to electrode 130 (and respecting flow division locus 132). Also, electrode 131 has a passage 133 with straight cylindrical conformation throughout its length. The separate coils 128 and 129 may be separately energized as at 134 and 135 to effect rotation of the arc attachment loci in the passages 136 and 137, for either radial or tangential injection as described in FIGS. 6 and 3.

The anode and cathode elements may have various other forms with flow passages that are diverging or converging conically in a downstream direction, or of nozzle configuration, or stepped or cylindrical (large or small). Symmetrical or unsymmetrical pairs of such electrodes may be used together as anode and cathode elements. Any electrically conducting materials may be used, if desirable, when compatible with proper cooling.

I claim:

1. In plasma processing apparatus, structure including electrode elements each forming a passage for passing the flow of gas therethrough and for reception of an arc discharge pattern penetrating said element passages in the path of said flow, said passages having opposed entrances and exits downstream of said entrances and means to conduct electrical current to said elements to create said are discharge pattern, said passage in at least one element including a relatively reduced cross section throat region directly downstream of the entrance of the element passage, and a relatively increased cross section diffuser region directly downstream of the throat, the arc having loci of attachment to at least one element at said diffuser region.

2. The combination of claim 1 in which said structure forms gas flow inlet porting extending between said cathode and anode elements and in such proximity to said passages that the inlet flow divides to enter said respective passages.

3. The combination of claim 2 in which said elements are annular and said passages extend downstream at opposite sides of the inlet flow division locus.

4. The combination of claim 2 in which said cathode and anode flow passages extend generally symmetrically with respect to said inlet flow division locus.

5. The combination of claim 3 in which said structure includes a ring having a series of inlet ports arranged to direct the inlet flow in -a spiral between said cathode and anode elements so that the flow tends to spiral upon appreaching said passages.

6. The combination of claim 3 including a housing containing said structure and forming therewith fluid coolant conduiting outside said passages.

7. The combination of claim 3 in which said last named means includes electrode plates contacting said cathode and anode elements proximate the downstream ends thereof.

8. The combination of claim 1 including means to introduce quench fluid into the path of hot gas flowing downstream relative to said loci of arc attachment.

9. The combination of claim 1 including means to combine the gas streams flowing downstream of said loci of arc attachment to the elements.

10. The combination of claim 1 in which said cathode and anode elements consist of principally copper.

11. The combination of claim 3 including means to variably control the downstream flow of gas from one of said elements.

12. The invention as defined in claim 3 including ducting -for delivering material into the arc in one of said passages at a point downstream of said flow division locus.

13. The combination of claim 2 in which said cathode and anode flow passages extend generally unsymmetrically with respect to said inlet flow division locus.

14. The combination of claim 2 in which the arc has loci of attachment to the anode and cathode elements, and including means to introduce quench fluid into the path of hot gas flowing downstream relative to the locus of arc attachment within at least one of said elements.

15. The combination of claim 3 in which at least one of said passages has straight cylindrical conformation throughout its length.

16. The combination of claim 1 in which the arc has loci of attachment to the anode and cathode elements, and including magnetic means to effect rotation of at least one of said attachment loci.

17. The combination of claim 1 in which the arc has loci of attachment to the anode and cathode elements, and including separate magnetic field coils to effect rotation of said attachment loci.

References Cited UNITED STATES PATENTS 2,892,114 6/ 1959 Kilpatrick 313-63 2,920,236 1/ 1960 Chambers et al. 176-2 2,960,614 11/1960 Mallinkrodt 31363 3,132,996 5/1964 Baker 1767 3,360,682 12/1967 Moore 3l3-161 FOREIGN PATENTS 31,337 1/1965 Germany. 1,395,362 3/ 1965 France. 1,097,053 1/ 1961 Germany. 1,153,463 8/ 1963 Germany.

' ROBERT K. MIHALEK. Primary Examiner. 

1. IN PLASMA PROCESSING APPARATUS, STRUCTURE INCLUDING ELECTRODE ELEMENTS EACH FORMING A PASSAGE FOR PASSING THE FLOW OF GAS THERETHROUGH AND FOR RECEPTION OF AN ARC DISCHARGE PATTERN PENETRATING SAID ELEMENT PASSAGES IN THE PATH OF SAID FLOW, SAID PASSAGES HAVING OPPOSED ENTRANCES AND EXITS DOWNSTREAM OF SAID ENTRANCES AND MEANS TO CONDUCT ELECTRICAL CURRENT TO SAID ELEMENTS TO CREATE SAID ARC DISCHARGE PATTERN, SAID PASSAGE IN AT LEAST ONE ELEMENT INCLUDING A RELATIVELY REDUCED CROSS SECTION THROAT REGION DIRECTLY DOWNSTREAM OF THE ENTRANCE OF THE ELEMENT PASSAGE, AND A RELATIVELY INCREASED CROSS SECTIION DIFFUSER REGION DIRECTLY DOWNSTREAM OF THE THROAT, THE ARC HAVING LOCI OF ATTACHMENT TO AT LEAST ONE ELEMENT AT SAID DIFFUSER REGION.
 16. THE COMBINATION OF CLAIM 1 IN WHICH THE ARC HAS LOCI OF ATTACHMENT TO THE ANODE AND CATHODE ELEMENTS, AND INCLUDING MAGNETIC MEANS TO EFFECT ROTATION OF AT LEAST ONE OF SAID ATTACHMENT LOCI. 